1. Field of the Invention
The present invention relates to a root canal length measuring apparatus and a root canal treatment apparatus which are used for dental treatment and diagnosis.
2. Description of the Background Art
As shown in FIG. 16, a human tooth is composed of an enamel 101, a dentin 102 and a cementum 103. The tooth is supported by an alveolar bone 104 and a gum 105. A dental pulp 106 is present inside the tooth, and blood vessels and nerves pass from the dental pulp 106 through a root canal 107 so as to be connected to blood vessels below the alveolar bone 104. Ends of the root canal 107 on side of the alveolar bones 104 are called as an apex 108.
A root membrane 109 is present on a boundary between a tooth root of the cementum 103 including the apex 108 and the alveolar bone 104. The root membrane 109 is a membrane which covers the entire tooth root of the tooth 101 as shown in FIG. 17. As shown in FIG. 17, the root canal has a portion which is called as an apical constriction 111 where the root canal becomes narrow near a lower portion 110 of the tooth. A shape of the apical constriction 111 varies between individuals, namely, some are curved and some are straight as shown in FIG. 17. In FIG. 17, an opening of the root canal on the robot membrane 109 side is called as an apical foramen 112.
In general, root canal treatment using a root canal length measuring apparatus and a root canal treatment apparatus is done in the following manner. A length of a root canal to be measured or treated is measured. The root canal is enlarged based on a result obtained by the measurement. Thereafter, the enlarged root canal is cleaned, and the enlarged root canal is filled with a predetermined material.
Specifically, in the root canal length measurement, as shown in FIG. 18, a measurement electrode 201 of a thin file (tool having diameter of 0.10 mm to 0.15 mm for enlarging a root canal) is inserted into a root canal 203 of a tooth 202, and an electric measuring signal is applied between the measurement electrode 201 and an oral electrode 204, so that an apex 205 is detected. After the apex 205 is detected, a working length is determined based on a position of the apex 205.
The method for applying the electric measuring signal between the measurement electrode 201 and the oral electrode 204 so as to detect the apex 205 includes a method using a change in impedance in the root canal as described below. When the measurement electrode 201 is in the position of the apex 205, the impedance value in the root canal is directly used based on a principle that an impedance value between the measurement electrode 201 and an oral mucosa becomes constant. In this method, however, the position of the apex 205 is a position where the measurement electrode 201 passes through an apical foramen 112 and comes in contact with the root membrane 109 as shown in FIG. 17.
There is also a method in which when the measurement electrode 201 is in the position of the apex 205, the apex is detected by using a difference in the impedance in the root canal based on a principle that a difference in the impedance in the root canal measured at two or more kinds of frequencies becomes constant. This method, however, occasionally requires such adjustment that the impedance value in the root canal is added to a difference in the impedance in the root canal.
When the measurement electrode 201 is on the position of the apex 205, the apex is detected by using a ratio of the impedance in the root canal based on a principle that the ratio of the impedance in the root canal measured at two or more kinds of frequencies becomes constant.
Besides the above methods, there is a method in which the ratio or the difference is not obtained, the apex is detected according to a calculating table which is prepared in advance where the impedance in the root canal measured at two or more kinds of frequencies is used as a pointer. The principle of this method is similar to those of the methods for obtaining the ratio and difference in the impedance in a root canal.
In the above methods, as shown in FIG. 18, a change in a measurement current flowing in a root canal is measured by a detecting resistor 206, so that the impedance in the root canal is obtained. In this technical field, the measurement of the impedance in a root canal is not limited to the direct measurement of the impedance, and thus includes measurement of an amount corresponding to the impedance. That is to say, measurement of a current value or a voltage value corresponding to the impedance is also included in the measurement of the impedance in a root canal. The above describes the apex detecting methods according to the measurement of the impedance in a root canal, but beside them, a method for detecting a change in a phase of an electric current or detecting a change in current density so as to detect an apex is occasionally adopted.
In the root canal enlargement, the file is gradually thickened to a position, which is 0.5 to 2 mm away from the apex detected by the root canal length measurement toward a tooth crown 207 side, as a reference position, so that the root canal is enlarged. Specifically, a root canal is enlarged by, for example, a step back method for enlarging the root canal up to a position 0.5 mm away from the apex using a file #20 (diameter: 0.2 mm), and up to a position 1.0 mm away from the apex using a file #30 (diameter: 0.3 mm), and up to a position 2.0 mm away from the apex using a file #40 (diameter: 0.4 mm).
In the root canal cleaning, contaminants in the enlarged root canal and chips generated at the time of the enlargement are rinsed. In the root canal filling, the root canal is filled with a predetermined substance so that the cleaned root canal is not reinfected.
A conventional root canal length measuring apparatus does not measure a root canal length itself but detects a position of the apex 205 shown in FIG. 18. For this reason, the conventional root canal length measuring apparatus has only a function for detecting the apex 205 but does not have a function for displaying to what extent a position of a tip of the measurement electrode 201 is away from the apex 205.
An indicator of a root canal length measuring apparatus described in Japanese Patent No. 3113095 shows arrival of the tip of the measurement electrode at the apex 205 by means of apex display as shown in FIG. 19. In FIG. 19, however, besides the apex display, a change in the measurement electrode position in the root canal can be displayed only as a guide. Scale marks 1 to 3 are given to the guide display, but this display does not show a distance from the apex 205 in the on-measuring root canal to the measurement electrode 201.
The feature of the root canal as one of human tissues is not constant because a shape of a root canal and an environment in a root canal varies. For this reason, the root canal measuring apparatus described in Japanese Patent No. 3113095 enables accurately reading from the indicator only whether or not the tip of the measurement electrode 201 has arrived at the apex 205 and whether the tip of the measurement electrode 201 is coming close to or is moving away from the apex 205.
As described in the background of the invention, the conventional root canal length measuring apparatus and the root canal treatment apparatus can accurately detect only the position of an apex. When the root canal treatment such as the root canal enlargement is done, however, it is occasionally necessary to accurately acquire positions in the root canal other than the apex. Particularly, it is important for the root canal treatment to knows a distance from the apex as a reference position at the time of the root canal enlargement, the position of the apical constriction, the position of the curved portion of the root canal, a position where pathologic changes such as breakage of a collateral, a perforated portion and a tooth root occur, and a position of a treatment difficult portion such as a step and a ledge.
In the case of the canal root enlargement treatment using a motor, in general, a motor driving method is changed on predetermined positions. In such a constitution, for example, the rotating speed of the motor per hour is reduced on a portion where the root canal is curved, and the motor is rotated reversely near an apex. For this reason, it is important to know the above positions with high reproducibility in the same root canal.